Rotary compressor

ABSTRACT

There is provided a two-stage compression rotary compressor in which the balancer mass of a rotor can be made as small as possible, and the moments that tilt the whole of a shaft can be balanced. The axial length L 2  of a high-stage side crankshaft  72  corresponding to a high-stage compressing section  32  is longer than the axial length L 1  of a low-stage side crankshaft  73  corresponding to a low-stage compressing section  31  (L 2 &gt;L 1 ).

TECHNICAL FIELD

The present invention relates to a rotary compressor having two-stagecompressing sections including a low-stage compressing section and ahigh-stage compressing section. More particularly, it relates to atechnique for preventing a deflection occurring on a shaft connecting amotor and the compressing section to each other to enhance thereliability.

BACKGROUND ART

Generally, in a rotary compressor, in order to reduce a loss ofrefrigerant caused by the leakage by sealing the gap of a compressionchamber and to lubricate sliding portions such as bearings, acompressing section is arranged in the lower part of a closed vessel inwhich lubricating oil accumulates.

Also, in a two-stage compression rotary compressor, in order to makebetter the balance of compressive load torques produced in twocompressing sections and the balance of centrifugal forces acting on theoff-center parts corresponding to the two compressing sections, that is,turning pistons and the off-center parts of a shaft engaging with thepistons, the compression phases of a low-stage compressing section and ahigh-stage compressing section are shifted through 180 degrees.

By the centrifugal forces acting on the two off-center parts of theshaft and the two turning pistons, a moment that tends to tilt the wholeof the shaft is produced. Therefore, a balancer is attached to above andbelow a rotor of a motor to cancel the moment that tends to tilt thewhole of the shaft.

In the two-stage compression rotary compressor, in terms of thecompression characteristics thereof, the volume of the high-stagecompressing section must be smaller than the volume of the low-stagecompressing section. As means for decreasing the volume of compressionchamber, there are available a method in which the thickness ofcompression chamber, that is, the thickness of a cylinder is decreasedand a method in which the turning radius of the piston is decreased. Inboth of these methods, the centrifugal forces acting on the off-centerparts of the shaft and the pistons are smaller in the high-stagecompressing section having a smaller volume than in the low-stagecompressing section having a larger volume.

Therefore, as described in Japanese Patent Application Publication No.H11-230073, there is known means for decreasing the mass of the balancerby arranging the low-stage compressing section, on which a largercentrifugal force acts, on the side close to the rotor to which thebalancer is attached, that is, by arranging the low-stage compressingsection above the high-stage compressing section.

However, in the case where the low-stage compressing section is arrangedabove the high-stage compressing section, there arises a problemdescribed below. Depending on the operation pressure condition and therotational speed condition of the compressor, the oil level oflubricating oil lowers from the compressing section arranged on theupper side in the closed vessel, and the compressing section on theupper side is exposed to refrigerant gas. Therefore, the refrigerantleaks into a suction chamber and the compression chamber passing througha gap between a vane and a vane groove, whereby a leakage loss iscreated.

If the low-stage compressing section is arranged on the upper side,since the interior of closed vessel has the discharge pressure of thehigh-stage compressing section, the difference in pressure between thesuction chamber and the compression chamber is large as compared withthe case where the high-stage compressing section is arranged on theupper side, so that the quantity of refrigerant leaking into the suctionchamber and the compression chamber through the gap increases, whichpresents a problem of further decreased efficiency of compressor.

Accordingly, an object of the present invention is to provide a rotarycompressor in which the mass of a balancer can be decreased, and therebythe deflection of a shaft is reduced, so that the seizure in bearingparts and the contact of a rotor with a stator can be prevented.

SUMMARY OF THE INVENTION

To achieve the above object, the present invention has some featuresdescribed below. A rotary compressor having a two-stage compressingsection including a low-stage compressing section and a high-stagecompressing section provided in a closed shell, and a motor for drivingthe two-stage compressing section, the high-stage compressing sectionbeing arranged on the motor side, is characterized in that when theaxial length of the off-center part of shaft corresponding to thelow-stage compressing section, that is, a low-stage side crankshaft, istaken as L1, and the axial length of the off-center part of shaftcorresponding to the high-stage compressing section, that is, ahigh-stage side crankshaft, is taken as L2, L2 is longer than L1.

According to this configuration, the mass of a balancer attached to arotor can be made small by making the axial length of the high-stageside crankshaft longer than that of the low-stage side crankshaft.Thereby, the deflection of the whole of the shaft is reduced, so thatseizure caused by a local excessive load of a bearing part and thecontact of the rotor with a stator can be prevented.

As a preferable mode, the rotary compressor is characterized in that therotational speed of the compressing section is variable. According tothis configuration, in the rotary compressor in which the rotationalspeed is variable, when the rotational speed is high, the centrifugalforces acting on an upper balancer and a lower balancer increase, bywhich the deflection of the shaft is increased, and therefore the effectof the present invention is further increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a rotary compressor inaccordance with one embodiment of the present invention;

FIG. 2 is a transverse sectional view of a compressing section of therotary compressor shown in FIG. 1;

FIG. 3 is a schematic view showing rotating parts of the rotarycompressor shown in FIG. 1 and centrifugal forces acting thereon; and

FIG. 4 is a schematic view showing a deflected state of a shaft formedby centrifugal forces of the rotary compressor shown in FIG. 1.

DETAILED DESCRIPTION

An embodiment of the present invention is explained with reference toFIG. 1. The present invention is not limited to this embodiment. Arotary compressor 1 includes a cylindrical closed vessel 2 arranged inthe vertical direction, a motor 4 provided in an upper part in theclosed vessel 2, and a compressing section 3 in a lower part therein.

The closed vessel 2 consists of a cylindrical main shell 21, adome-shaped top shell 22 that closes the upper end part of the mainshell 21, and a dome-shaped bottom shell 23 that closes the lower endpart of the main shell 21. The top shell 22 and the bottom shell 23 arefixed to the main shell 21 by welding.

The top shell 22 is provided with a refrigerant discharge pipe 24 fordischarging the refrigerant having been discharged into the closedvessel 2 from the compressing section 3 to the outside of the closedvessel 2.

A stator 41 of the motor 4 is shrinkage fitted to the main shell 21. Arotor 42 of the motor 4 is shrinkage fitted onto a shaft 7 mechanicallyconnecting the motor 4 to the compressing section 3. Above and below therotor 42, an upper balancer 43 and a lower balancer 44 are attached,respectively, to balance the centrifugal forces of the whole of rotatingparts.

The compressing section 3 is provided with a high-stage compressingsection 32 in the upper part thereof and a low-stage compressing section31 in the lower part thereof. The discharge side of the low-stagecompressing section 31 and the suction side of the high-stagecompressing, section 32 are connected to each other by an intermediateconnection pipe 26 on the outside of the closed vessel 2, by which atwo-stage compressing section is formed.

Next, the configuration of each section of the compressing section 3 isexplained with reference to FIG. 2. FIG. 2 shows the transverse crosssection of the low-stage compressing section 31 shown in FIG. 1. Theconfiguration of the high-stage compressing section 32 is the same asthat of the low-stage compressing section 31 except that the pistons are180° out-of-phase.

Each of the compressing sections 31 and 32 has a cylinder 200, 400 and acylindrical piston 220, 420 accommodated in a cylindrical cylinder bore200 a, 400 a formed on the inside of the cylinder 200, 400. Between theinternal wall of the cylinder bore 200 a, 400 a and the outer peripheralsurface of the piston 220, 420, a working space for refrigerant isformed.

The cylinder 200, 400 is provided with a cylinder groove 200 b, 400 bdirected from the cylinder bore 200 a, 400 a toward the outer peripherydirection, and has a flat plate shaped vane 230, 430 in the cylindergroove 200 b, 400 b.

Between the vane 230, 430 and the internal wall of the closed vessel 2,a spring 240, 440 is provided. By the urging force of the spring 240,440, the tip end of the vane 230, 430 is brought into sliding contactwith the outer wall of the piston 220, 420, by which the working spaceis divided into a suction chamber V1, V2 and a compression chamber C1,C2.

In order to make the working space volume of the high-stage compressingsection 32 smaller than that of low-stage compressing section 31, eachof the cylinder 200, the piston 220, and the vane 230 on the high-stageside has a smaller thickness in the axial direction than each of thecylinder 400, the piston 420, and the vane 430 on the low-stage side.

Next, referring again to FIG. 1, the whole of the compressor 1 isexplained. The compressor 1 has a main frame 100 above the high-stageside cylinder 200, an intermediate partition plate 300 between thehigh-stage side cylinder 200 and the low-stage side cylinder 400, and asub-frame 500 below the low-stage side cylinder 400, and the upside andthe downside of each of the two working spaces are closed by the mainframe 100, the intermediate partition plate 300, and the sub-frame 500,whereby each of the two working spaces is formed into a closed space.

Above the main frame 100, a high-stage side discharge muffler cover 130is provided, and a high-stage side discharge muffler chamber M2 forreducing the pressure pulsation of discharged refrigerant is formed.Below the sub-frame 500, a low-stage side discharge muffler cover 510 isprovided, and a low-stage side discharge muffler chamber M1 for reducingthe pressure pulsation of discharged refrigerant is formed.

The high-stage side discharge muffler cover 130, the main frame 100, thehigh-stage side cylinder 200, the intermediate partition plate 300, thelow-stage side cylinder 400, the sub-frame 500, and the low-stage sidedischarge muffler cover 510 are fixed integrally with bolts (not shown),and further the outer peripheral part of the main frame 100 is fixed tothe main shell 21 by spot welding.

The main frame 100 and the sub-frame 500 have bearing parts 110 and 502,respectively, so that the shaft 7 is fitted in the bearing parts 110 and502 so as to be rotatably supported.

The shaft 7 has two crankshafts 72 and 73 that are off-centered in the180° different direction. One crankshaft 72 engages with the piston 220of the high-stage compressing section 32, and the other crankshaft 73engages with the piston 420 of the low-stage compressing section 31.

Along with the rotation of the shaft 7, the pistons 220 and 420 turnwhile slidingly contacting with the inside walls of the respectivecylinder bores 200 a and 400 a, and following this turning motion of thepistons 220 and 420, the vanes 230 and 430 reciprocate, by which thevolumes of the suction chambers V1 and V2 and the compression chambersC1 and C2 are changed continuously. Thus, the compressing section 3repeats the suction and compression of refrigerant.

The suction chamber V1 of the low-stage compressing section 31 isconnected to a refrigerant suction pipe 64 via a low-stage side suctionhole 410 provided in the cylinder 400. The compression chamber C1 of thelow-stage compressing section 31 is connected to the intermediateconnection pipe 26 via a low-stage side discharge hole 520 provided inthe sub-frame 500 and the low-stage side discharge muffler chamber M1.

More specifically, the low-stage side discharge hole 520 is providedwith a check valve 540. Also, the refrigerant suction pipe 64 isconnected to the low-stage side suction hole 410 via a low-stage sidesuction connection pipe 411, and the intermediate connection pipe 26 isconnected to the low-stage side discharge muffler chamber M1 via anintermediate discharge connection pipe 521.

The suction chamber V2 of the high-stage compressing section 32 isconnected to the intermediate connection pipe 26 via a high-stage sidesuction hole 210 provided in the cylinder 200. The compression chamberC2 of the high-stage compressing section 32 is open to the interior ofthe closed vessel 2 via a high-stage side discharge hole 120 provided inthe main frame 100 and the high-stage side discharge muffler chamber M2.

More specifically, the high-stage side discharge hole 120 is providedwith a check valve 140. Also, the intermediate connection pipe 26 isconnected to the high-stage side suction hole 210 via an intermediatesuction connection pipe 211.

At the side of the body of the compressor 1, an accumulator 6 consistingof an independent closed vessel 61 is provided. Above the accumulator 6,a refrigerant return pipe 62 is provided, the refrigerant return pipe 62being connected to a heat pump system, not shown. Below the accumulator6, there is provided the refrigerant suction pipe 64 one end having an Lshape of which is extended to the upper part in the accumulator 6 andthe other end of which is connected to the suction chamber V1 of thelow-stage compressing section 31 from the side surface of the compressor1.

Next, the flow of refrigerant in the above-described configuration isexplained with reference to FIGS. 1 and 2. The refrigerant flowing fromthe heat pump system side into the accumulator 6 passing through therefrigerant return pipe 62 is separated so that a liquid refrigerantlies in the lower part of the accumulator 6 and a gas refrigerant liesin the upper part thereof.

When the low-stage side piston 420 is turned to increase the volume ofthe low-stage side suction chamber V1, the gas refrigerant in theaccumulator 6 is sucked into the low-stage side suction chamber V1 ofthe compressor body 1 through the refrigerant suction pipe 64.

After one turn of the piston 420, the low-stage side suction chamber V1comes to a position isolated from the low-stage side suction hole 410,and is turned to the low-stage side compression chamber C1 as it is, bywhich the refrigerant is compressed.

When the pressure of the compressed refrigerant reaches the pressure inthe low-stage side discharge muffler chamber M1 on the outside of thecheck valve 540 provided in the low-stage side discharge hole 520, thatis, an intermediate pressure, the check valve 540 is opened, by whichthe compressed refrigerant is discharged into the low-stage sidedischarge muffler chamber M1.

After the pressure pulsation of refrigerant, which may cause noise, hasbeen reduced in the low-stage side discharge muffler chamber M1, therefrigerant is guided into the suction chamber V2 of the high-stagecompressing section 32 through the intermediate connection pipe 26.

The refrigerant guided into the suction chamber V2 of the high-stagecompressing section 32 is sucked, compressed, and discharged in thehigh-stage compressing section 32 on the same principle as that of thelow-stage compressing section 31. After the pressure pulsation ofrefrigerant has been reduced in the high-stage side discharge mufflerchamber M2, the refrigerant is discharged into the closed vessel 2.

The refrigerant is further guided to a portion above the motor 4 afterpassing through a core notch (not shown) in the stator 41 of the motor 4and a gap between a core and a coil, and is discharged to the systemside through the discharge pipe 24.

Next, the centrifugal forces acting on the rotating parts in thecompressor configured as described above are explained with reference toFIG. 3.

FIG. 3 is a schematic view extractingly showing the rotating parts inthe compressor.

As the centrifugal forces acting on the rotating parts, there aregenerated a centrifugal force (F1) acting on the low-stage sidecrankshaft 73 and the low-stage side piston 420 engaging therewith, acentrifugal force (F2) acting on the high-stage side crankshaft 72 andthe high-stage side piston 220 engaging therewith, a centrifugal force(F4) acting on the upper balancer 43 attached to above the rotor 42, anda centrifugal force (F3) acting on the lower balancer 44 attached tobelow the rotor 42. To balance these centrifugal forces in thehorizontal direction, the following equation holds.

F1+F4=F2+F3  (1)

To balance moments that tend to tilt the whole of shaft, Equation (2) isobtained from the moment around the application point of F3.

F1×(Lx+Ly)=F2×Ly+F4×Lz  (2)

F3 and F4, that is, the mass of the upper balancer 43 of the rotor 42and the mass of the lower balancer 44 thereof are determined so as tosatisfy Equation (2).

Rearranging Equation (2) gives

F4=(F1×(Lx+Ly)−F2×Ly)/Lz  (3)

From Equation (3), it can be seen that F4 can be decreased as F1 isdecreased or F2 is increased.

That is to say, the upper balancer 43 of the rotor 42 can be madesmaller as the mass of the low-stage side crankshaft 73 is decreased orthe mass of the high-stage side crankshaft 72 is increased.

Hereunder, the state in which the shaft 7 is deflected by thecentrifugal forces acting on the shaft 7 is explained with reference toFIG. 4.

FIG. 4 is a schematic view extractingly showing the shaft 7 and thebearing part 110 supporting the shaft 7.

If the deflection of the whole of the shaft 7 increases, especially inthe bearing part 110 of the main frame 100, the shaft 7 deformsexceeding the gap between the shaft 7 and the bearing part 110, andcomes locally into contact with the bearing part 110 at the upper orlower part of the bearing part 110, which may cause seizure.

To solve this problem, the axial length of the high-stage sidecrankshaft 72 is made longer than the axial length of the low-stage sidecrankshaft 73. Thereby, the upper balancer 43 of the rotor 42 can bemade small, so that the deflection of the whole of the shaft 7 isreduced, whereby seizure caused by a local excessive load of the bearingpart 110 and the contact of the rotor 42 with the stator 41 can beprevented.

On the other hand, the effect described below can be achieved. In thecompressor used for a heat pump for an air conditioner, a water heater,and the like, the suction pressure Ps and the discharge pressure Pd ofthe compressor change mainly depending on the outside air temperaturecondition. This fact means that the compression ratio φ (=Pd/Ps) as thewhole of compressor is not constant, so that it is necessary to respondto a wide range.

Taking the suction volume of the low-stage compressing section 31 as V1,the suction volume of the high-stage compressing section 32 as V2, andthe specific heat of compressed gas as κ, in the case where losses inthe compressing sections 31 and 32 are neglected, the compression ratioφ1 of the low-stage compressing section 31 is expressed asφ1=(V1/V2)^(κ). That is to say, the compression ratio φ1 of thelow-stage compressing section 31 is determined by the suction volumes ofthe two cylinders without depending on the outside air temperaturecondition.

Therefore, under the condition in which the total compression ratio φ ishigh, for example, in a cooling operation under a condition in which theoutside air temperature is especially high or in a heating operationunder a condition in which the outside air temperature is especiallylow, the compression ratio φ2 of the high-stage compressing section 32is high necessarily.

That is to say, under such a condition, the load torque of thehigh-stage compressing section 32 is higher than that of the low-stagecompressing section 31. To support this load, the length of crankshaftnot shorter than a predetermined length is necessary. However, theincrease in length of crankshaft achieved than necessary is unfavorablebecause it may cause an increase in slide loss in a crank part.

Therefore, as described above, the axial length L2 of the high-stageside crankshaft is made longer than the axial length L1 of the low-stageside crankshaft (L2>L1). Thereby, both of the improvement in reliabilityin the crankshaft bearing parts and the improvement in efficiency due tothe reduction in slide loss can be achieved.

In this embodiment, the rotary compressor 1 configured so that in thecompressor provided with the two-stage compression type compressingsection having the low-stage compressing section 31 and the high-stagecompressing section 32, the working space volume of the high-stagecompressing section 32 is made smaller than that of the low-stagecompressing section 31 by making the axial length of the high-stagecompressing section 32 shorter than that of the low-stage compressingsection 31 has been shown typically as a preferred mode. However theconfiguration of the rotary compressor 1 may be such that the workingspace volume of the high-stage compressing section 32 is made smaller bymaking the axial lengths of the low-stage compressing section 31 and thehigh-stage compressing section 32 equal to each other and by making theturning radius of the high-stage side piston 220 smaller than that ofthe low-stage side piston 420.

Also, the rotary compressor 1 may be a two-stage compression rotarycompressor configured so that a gas injection cycle is used as therefrigerating cycle, and an injection refrigerant is allowed to flowinto an intermediate compressing section between the low-stagecompressing section 31 and the high-stage compressing section 32.

Also, the compressing mechanism of the compressing section 3 is notlimited to the compressing mechanism shown in this embodiment if thecompressor is configured so that the change in volumes of the suctionchamber V1, V2 and the compression chamber C1, C2 caused by the turningmotion of the piston 220, 420 imparted by the crankshaft 72, 73 isutilized.

The present application is based on, and claims priority from, JapaneseApplications Serial Number JP2007-083399, filed Mar. 28, 2007 thedisclosure of which is hereby incorporated by reference herein in itsentirety.

1. A rotary compressor comprising: a closed vessel; a low-stagecompressing section and a high-stage compressing section provided in theclosed vessel; a shaft provided with a low-stage side off-center partand a high-stage side off-center part corresponding to the low-stagecompressing section and the high-stage compressing section,respectively; a motor connected mechanically to the shaft to drive thelow-stage compressing section and the high-stage compressing section,each of the low-stage compressing section and the high-stage compressingsection having a cylinder; a piston turning in the cylinder whileengaging with the off-center part of the shaft; and a vane the tip endof which comes into sliding contact with the piston while the vanereciprocates in a vane groove in the cylinder to form a suction chamberand a compression chamber for refrigerant together with the cylinder andthe piston, and further comprising: an intermediate partition plate heldbetween the low-stage compressing section and the high-stage compressingsection to close one end surface of the suction chamber and thecompression chamber; and a main frame and a sub-frame each of which isprovided with a bearing part for rotatably supporting the shaft andcloses one end surface of the suction chamber and the compressionchamber, in which means for allowing the discharge side of the low-stagecompressing section and the suction side of the high-stage compressingsection to communicate with each other is provided, whereby a two-stagecompressing section is formed, wherein when the axial length of theoff-center part of shaft corresponding to the low-stage compressingsection is taken as L1, and the axial length of the off-center part ofshaft corresponding to the high-stage compressing section is taken asL2, L2 is longer than L1.
 2. The rotary compressor according to claim 1,wherein the rotational speed of the compressing section is variable.